Heavy duty diesel engine lubricating oil compositions

ABSTRACT

The use of an effective amount of one or more compounds capable of reducing friction coefficients under mixed lubrication or boundary lubrication conditions in a heavy duty diesel engine lubricating oil composition for improving the fuel economy of a heavy duty diesel engine.

[0001] The present invention concerns the use of one or more compoundscapable of reducing friction coefficients under mixed lubrication orboundary lubrication conditions in heavy duty diesel engine lubricatingoil compositions. It also relates to such lubricating oil compositionswhich have been found to give improved fuel economy in operation ofheavy duty diesel engines.

[0002] The heavy duty trucking market employs the diesel engine as itspreferred power source due to its excellent longevity, and specializedlubricants have been developed to meet the more stringent performancerequirements of such heavy duty diesel engines.

[0003] Also, several engine tests are required to demonstratesatisfactory heavy duty performance, including the Cummins M11 test toevaluate soot-related valve train wear, filter plugging and sludge.

[0004] The fuel consumption of heavy duty diesel engines is of greatimportance to fleet operators since fuel costs constitute up to 30% ofoperating costs. Use of fuel-efficient lubricating oil compositionswould therefore help to reduce fuel consumption: even a 1% reductionwould lead to significant cost savings.

[0005] R. I Taylor states in “Heavy Duty Diesel Engine Fuel Economy:Lubricant Sensitivities” 00FL-309, SAE 2000 Millennium Publication“Advances in Powertrain Tribology”, SAE 2000, that, because heavy dutydiesel engines operate more under hydrodynamic conditions than passengercar engines, friction reducers will not be effective in reducing enginefriction losses in heavy duty diesel engines. This conclusion issupported by Stauffer et al in Lubrication Engineering, December 1984,pp.744-751; and by Kagaya et al in SAE 811412.

[0006] It has now been found, in contrast, that friction reducers areeffective in improving the fuel economy performance of heavy duty dieselengines. Accordingly, in a first aspect the present invention providesthe use of an effective amount of one or more compounds capable ofreducing friction coefficients under mixed lubrication or boundarylubrication conditions in a heavy duty diesel engine lubricating oilcomposition for improving the fuel economy of a heavy duty dieselengine.

[0007] In a second aspect, the present invention provides a heavy dutydiesel engine lubricating oil composition comprising an oil oflubricating viscosity, in a major amount, and added thereto:

[0008] (A) an effective amount of one or more compounds capable ofreducing friction coefficients under mixed lubrication or boundarylubrication conditions;

[0009] (B) a minor amount of a detergent composition comprising a metalsalt of an aromatic carboxylic acid; and

[0010] (C) a minor amount of a dispersant additive;

[0011] provided that the lubricating oil composition has a nitrogencontent, preferably derived from the dispersant additive, of at least0.06 mass %, based on the mass of the composition.

[0012] In a third aspect, the present invention provides a heavy dutydiesel engine additive concentrate composition comprising a diluent andone or more additives comprising:

[0013] (A) one or more compounds capable of reducing frictioncoefficients under mixed lubrication or boundary lubrication conditions;

[0014] (B) a detergent composition comprising a metal salt of anaromatic carboxylic acid; and

[0015] (C) a dispersant additive;

[0016] each in such a proportion as to provide a heavy duty dieselengine lubricating oil composition as defined in the second aspect whenthe oil composition contains 2 to 20 mass % of the additives.

[0017] In a fourth aspect, the present invention provides combination ofa heavy duty diesel engine in a land-based vehicle, which engine has atotal displacement of at least 6.5 litres and a displacement percylinder of at least 1.0 litre per cylinder and a lubricating oilcomposition as defined in the second aspect.

[0018] In a fifth aspect, the present invention provides a method oflubricating a heavy duty diesel engine in a land-based vehicle, whichengine has a total displacement of at least 6.5 litres and adisplacement per cylinder of at least 1.0 litre per cylinder, whichmethod comprises supplying to the engine a lubricating oil compositionas defined in the second aspect.

[0019] The American Petroleum Institute (API), Association desConstructeur Europeén d'Autombile (ACEA) and Japanese StandardsOrganisation (JASO) specify the performance level required forlubricating oil compositions. Also there are performance specificationsknown as Global, which contains tests and performance levels from ACEA,API and JASO specifications.

[0020] Thus, a heavy duty lubricating oil composition of the presentinvention preferably satisfies at least the performance requirements ofheavy duty diesel engine lubricants, such as at least the API CF-4 orAPI CG-4; preferably at least the API CH-4; especially at least the APICI-4. In another embodiment, the lubricating oil composition of theinvention, independently of meeting the API performance requirements,preferably satisfies at least the ACEA E2-96; more preferably at leastthe ACEA E3-96; especially at least ACEA E4-99; advantageously at leastthe ACEA E5-99. In a further embodiment, the lubricating oil compositionof the invention, independently of meeting the API and ACEA performancerequirements, preferably satisfies the JASO DH-1 or Global DHD-1.

[0021] The features of the present invention will now be discussed inmore detail.

[0022] Heavy Duty Diesel Engines

[0023] Heavy duty diesel engines according to the present invention areused in land-based vehicles, preferably large road vehicles, such aslarge trucks. The road vehicles typically have a weight greater than 12tonnes. The engines used in such vehicles tend to have a totaldisplacement of at least 6.5, preferably at least 8, more preferably atleast 10, such as at least 15, litres; engines having a totaldisplacement of 12 to 20 litres are preferred. Generally, engines havinga total displacement greater than 24 litres are not consideredland-based vehicles. The engines according to the present invention alsohave a displacement per cylinder of at least 1.0 or at least 1.5, suchas at least 1.75, preferably at least 2, litres per cylinder. Generally,heavy duty diesel engines in road vehicles have a displacement percylinder of at most 3.5, such as at most 3.0; preferably at most 2.5,litres per cylinder. The term “heavy duty” in relation to internalcombustion engines is known in the art: see ASTM D4485 at §3.17 whereheavy duty engine operation is characterised by average speeds, poweroutputs and internal temperatures that are generally close to potentialmaximums; therefore, a heavy duty diesel engine is considered to operategenerally under such conditions.

[0024] As used herein, the terms ‘total displacement’ and ‘displacementper cylinder’ are known to those skilled in the art of internalcombustion engines (see “Diesel Engine Reference Book”, edited by B.Challen and R. Baranescu, second edition, 1999, published by SAEInternational). Briefly, the term “displacement’ corresponds to thevolume of the cylinder in the engine as determined by the pistonmovement and consequently the “total displacement” is the total volumedependent on the number of cylinders; and the term ‘displacement percylinder’ is the ratio of the total displacement to the number ofcylinders in the engine.

[0025] Lubricating Oil Composition

[0026] In each aspect of the invention, the lubricating oil compositionpreferably has less than 0.13, or less than 0.1, or less than 0.09, orless than 0.08, or less than 0.07 or less than 0.06, mass % ofphosphorus based on the mass of the oil composition; more preferably ithas at most 0.05, or at most 0.04 or at most 0.03, mass %; such as inthe range from 0.001 to 0.03 mass %; for example at most 0.02 or at most0.01 mass %. In a preferred embodiment of each aspect, the phosphoruscontent of the lubricating oil composition is zero.

[0027] In each aspect of the invention, the lubricating oil compositionpreferably has, independently of the amount of phosphorus, at most 1.0,or at most 0.75, or at most 0.50, or at most 0.45, or at most 0.4, or atmost 0.35, or at most 0.3, or at most 0.25, mass % of sulfur based onthe mass of the oil composition; especially it has at most 0.2 or atmost 0.15, mass %; such as in the range from 0.001 to 0.1 mass %. In apreferred embodiment of each aspect, the sulfur content of thelubricating oil composition is zero.

[0028] The amount of phosphorus and sulfur in the lubricating oilcomposition is each measured according to ASTM D5185.

[0029] In an embodiment of each aspect of the invention, the amount ofphosphorus and sulfur is derived from an anti-wear additive, such as azinc dithiophosphate.

[0030] The lubricating oil composition of the invention can be in theviscometric form of any one of SAE 20W-X, SAE 15W-X, SAE 10W-X, SAE 5W-Xand SAE 0W-X, where X represents any one of 20, 30, 40 and 50; thecharacteristics of the different viscometric grades can be found in theSAE J300 classification. In an embodiment of each aspect of theinvention, independently of the other embodiments, the lubricating oilcomposition is in the form of an SAE 5W-X or SAE 0W-X lubricating oilcomposition, wherein X represents any one of 20, 30, 40 and 50.Preferably X is 20 or 30.

[0031] It has also found that the lubricating oil compositions of theinvention can meet the wear protection needed by heavy duty dieselengines, for example, by satisfying the requirements of the Cummins M11test to evaluate soot- related valve train wear. Thus, the heavy dutydiesel engine lubricating oil compositions of the present invention,particularly low viscosity lubricating oil compositions, such as SAE5W-X or SAE 0W-X lubricants, where X is as defined above, provideimproved fuel economy and also improved wear protection to the heavyduty diesel engine.

[0032] Thus, in a preferred embodiment of each aspect of the presentinvention, the heavy duty diesel engine lubricating oil composition,preferably in the form of an SAE 5W-X or SAE 0W-X oil composition,comprises one or more compounds capable of reducing frictioncoefficients under mixed lubrication or boundary lubrication conditions,and has a base blend viscosity of at least 8.2, such as from 8.5 to 30,preferably 8.5 to 10, mm²s⁻¹ at 100° C.

[0033] As used herein, the term “base blend viscosity” refers to theviscosity at 100° C., measured according to ASTM D445, of a compositioncomprising, or an admixture of, components that exhibit Newtonianbehaviour, which in the present invention are all of the components(including the carrier oil such as the basestock) but excluding thesolid polymer or ‘active ingredient’ of the viscosity modifier, which isconsidered not to exhibit Newtonian behaviour. Thus, the base blendviscosity can refer to the viscosity of a composition comprisingbasestock oil, dispersant, detergent, ZDDP, antioxidant, all carrieroils and diluent oils of the components, pour depressant and any othercomponents which exhibit Newtonian behaviour, such as anti-foamants.

[0034] Computer modeling systems may also be employed to predict thebase blend viscosity of a lubricating oil composition based on theviscosity of the components present therein. Alternatively, the baseblend viscosity may be measured by removing the polymer of the viscositymodifier from the lubricating oil composition and then measuring theviscosity of the resulting composition. Alternatively, the base blendviscosity may be determined by measuring the viscosity of thelubricating oil composition at a high shear rate, which shear ratecorresponds to the rate that does not affect the viscosity of the oilcomposition, generally such rates are greater than 10⁷ s⁻¹.

[0035] It has been found that lubricating oil compositions having thedefined base blend viscosity parameter and one or more of the definedcompounds will provide improved fuel economy and pass at least the ACEAE5-99 and/or the API CH-4 specification limits for the Cummins M11 200hour cross-head wear test.

[0036] In a preferred embodiment of each aspect of the presentinvention, the oil composition has less than 2 mass % of ash, preferablyless than 1.5 mass %, especially less than 1 mass %; such as in therange from 0 to 0.5 mass % ash, according to method ASTM D874.

[0037] Oil of Lubricating Viscosity

[0038] The lubricating oil can be a synthetic or mineral oil oflubricating viscosity selected from the group consisting of Group I, II,III, IV or V basestocks and mixtures thereof.

[0039] Basestocks may be made using a variety of different processesincluding but not limited to distillation, solvent refining, hydrogenprocessing, oligomerization, esterification and rerefining.

[0040] API 1509 “Engine Oil Licensing and Certification System”,Fourteenth Edition, December 1996 states that all basestocks are dividedinto five general categories:

[0041] Group I basestocks contain less than 90% saturates and/or greaterthan 0.03% sulfur and have a viscosity index greater than or equal to 80and less than 120;

[0042] Group II basestocks contain greater than or equal to 90%saturates and less than or equal to 0.03% sulfur and have a viscosityindex greater than or equal to 80 and less than 120;

[0043] Group III basestocks contain greater than or equal to 90%saturates and less than or equal or 0.03% sulfur and have a viscosityindex greater than or equal to 120;

[0044] Group IV basestocks contain polyalphaolefins (PAO); and

[0045] Group V basestocks contain all other basestocks not included inGroup I, II, III or IV.

[0046] Group IV basestocks, i.e. polyalphaolefins (PAO), includehydrogenated oligomers of an alpha-olefin, the most important methods ofoligomerization being free radical processes, Ziegler catalysis,cationic, and Friedel-Crafts catalysis.

[0047] Preferably the lubricating oil is selected from any one of GroupI to V basestocks.

[0048] Especially preferred is Group II, III, IV or V basestocks or anytwo or more mixtures thereof, or mixtures of Group IV basestocks with 5to 80 mass % of Group I, II, III or V basestocks, such as a fullysynthetic mixture of Group IV basestocks and Group V basestocks.

[0049] The test methods used in defining the above groups are ASTM D2007for saturates; ASTM D2270 for viscosity index; and one of ASTM D2622,4294, 4927 and 3120 for sulfur.

[0050] Compounds

[0051] Compounds capable of reducing friction coefficients under mixedlubrication or boundary lubrication conditions, such as in high pressureand sliding contacts, are known as friction reducers and a skilledperson would be able to identify such compounds using tests known in theart, for example tests carried out in a high frequency reciprocatingrig. Examples of contacts where high pressure and sliding conditionsoccur are in the valve train, piston ring liners and journal bearings.

[0052] A class of friction reducers is provided by polar compounds thatare capable of being adsorbed on metal surfaces, which compounds have apolar head- group and an oleophilic hydrocarbyl chain. These can bebroadly divided into two categories, i.e. (A) nitrogen-containingcompounds, such as amines, imides and amides, and (B) oxygen-containingcompounds, such as fatty acids and full or partial esters thereof.

[0053] The nitrogen-compounds (A) are suitably selected from the groupconsisting of (i) alkylene amines, especially the monoalkylene diamines,the dialkylene triamines and/or the polyalkylene polyamines,N,N′-dimethyl ethylene diamine which in turn may carry further alkyland/or hydroxy substituents; (ii) the alkanolamines, especially theN-alkyl derivatives of alkanolamines, such as ethanolamine,propanolamine, isopropanolamine and butanolamine in which the N-alkylgroups have from 1 to 20 carbon atoms, preferably 12 to 18 carbon atoms,the N,N-dialkanolamines, the N-alkyleneaminoalkyl dialkanolamines, andthe di(polyalkyleneoxy) alkanolamines; (iii) the alkyl amides in whichthe N-alkyl groups have from 1 to 25 carbon atoms, preferably 12 to 22carbon atoms; and (iv) the alkanolamides, especially the mono- anddi-alkanolamides of alkyl carboxylic acids and the (polyalkyleneoxy)alkanolamides. Specific examples of nitrogen-containing organic frictionreducers falling into the above categories are:

[0054] (i) the monoethylene diamines, diethylene triamines, thetriethylene tetraamines and the tetraethylene pentamines, and theN-alkyl derivatives thereof, e.g. Duomeen®T, andN,N′-di(l-hydroxyl-1,1-dimethyl methyl) ethylene diamine, i.e. Kaneda®No. 6;

[0055] (ii) N-alkyl or the appropriate N,N-dialkyl derivatives ofethanol amines, diethanol amines, propanol amines, iso-propanol amines,butanol amines, the N-alkyleneaminoalkyl ethanolamine in which the alkylgroup has 10 to 20 carbon atoms, di(polyalkyleneoxy) alkanolamines inwhich the total number of alkyleneoxy groups may range from 2 to 20,preferably from 5 to 15 groups, especially N-methyl ethanolamine(Kaneda® No.1), N-hydrocarbyl diethanolamine (Kaneda® No. 2B), N,N-dibutyl ethanolamine (Kaneda® No. 4), N-dodecyl diethanolamine(Ethomeen®C12), N-hydrocarbyl diethanolamine (Ethomeen®S12),N-trimethyleneaminoalkyl diethanolamine in which the alkyl group has 12to 18 carbon atoms (Ethoduomeen®), the N-alkyl-di (polyalkyleneoxy)diethanolamines which respectively have 5, 10 and 15 polyethyleneoxygroups (Tamno®-5, -10 and -15 respectively), and N,N′-dihydroxyethylethylenediamine (Kaneda®No.5);

[0056] (iii) the alkyl amides in which the alkyl groups have from 1 to30 carbon atoms, preferably from 5 to 20 carbon atoms and in which thealkyl groups may be straight or branched chain groups, such asArmoslip®CP-P and Armoslip®E in which the alkyl groups have 17 and 21carbon atoms respectively;

[0057] (iv) ethanolamides, the diethanolamides and the (polyalkyleneoxy)ethanolamides, and the N-alkyl derivatives thereof wherein the N-alkylgroup has from 1 to 25 carbon atoms, preferably from 5 to 20 carbonatoms and wherein in the case of the (polyalkyleneoxy) ethanolamidessaid amides having from 5 to 20 polyoxyalkylene groups, such asN-acylethanol amine, e.g. Kaneda® No. 9 (in which the alkyl group in theacyl moiety has 12 carbon atoms), diethanolamines e.g. Amizole® ISDE (inwhich the alkyl group in the acyl moiety has 18 carbon atoms), Kaneda®No.10 (in which the alkyl group in the acyl moiety has 12 carbon atoms),di(polyethyleneoxy) ethanol amide wherein the acyl group in the acylmoiety has 17 carbon atoms and the total number of polyethyleneoxygroups in the molecule is 5 (e.g. Tamdo®-5).

[0058] Especially preferred examples are compounds of oleic acid andtetraethylene pentamine, ethoxylated tallow amines and ethoxylatedtallow ether amines. Also useful are organo-metallic compounds ofhydrocarbyl amine compounds, such as disclosed in GB-A-882,295. Aminesmay be used as such or in the form of an adduct or reaction product witha boron compound such as a boric oxide, boron halide, metaborate, boricacid or a mono-, di- or trialkyl borate.

[0059] Examples of oxygen-containing organic friction reducers (B) arecarboxylic acids having 1 to 25 carbon atoms, such as stearic acid andoleic acids, preferably from 12 to 17 carbon atoms; full and partialesters thereof of di- and/or polyhydric alcohols, such as glycerol,trimethylol propane, pentaerythritol and polyhydroxy pyrans; and metalsalts thereof, e.g. metal stearates and metal oleates, wherein the metalis selected from transition metals (e.g. zinc), Group 1 metals and Group2 metals (e.g. calcium). Specific examples of oxygen-containing organicfriction reducers (B) are the mono-, di- an tri-esters of glycerol withan alkyl carboxylic acid, such as oleic acid; the correspondingpentaerythritol esters, such as the oleates, especially themono-oleates; and the monoester of 1-methylenehydroxy-2, 3, 4-trihydroxypyran, in which the methylene hydroxy group has been esterified withacetic acid. Esters of carboxylic acids and anhydrides with alkanols aredescribed in U.S. Pat. No. 4,702,850.

[0060] Examples of other conventional friction reducers are described byM. Belzer in the “Journal of Tribology” (1992), Vol.114, pp. 675-682 andM. Belzer and S Jahanmir in “Lubrication Science” (1988), Vol, pp. 3-26.

[0061] Oil-soluble additives which deposit molybdenum disulfide are alsoeffective friction reducers, such as oil-soluble or oil-dispersiblemolybdenum compounds.

[0062] Examples of organic molybdenum compounds include molybdenumxanthates, thioxanthates, alkoxides, carboxylates (such as, derivativesof polyhydroxy fatty esters, e.g. MOLYVAN® 855),dialkyldithiocarbamates, dialkyldithiophosphinates anddialkyldithiophosphates.

[0063] The molybdenum compound may, for example, be mononuclear,dinuclear, trinuclear or tetranuclear.

[0064] Dinuclear molybdenum compounds can be represented by the formulaMo₂O_(x)S_(4−x)L₂, where L is a ligand such as dialkyldithiocarbamateand dialkyldithiophosphate, and x is an integer from 0 to 4. An exampleof dinuclear (or dimeric) molybdenum dialkyldithiocarbamate is expressedby the following formula:

[0065] where R₁ to R₄ independently denote a straight chain, branchedchain or aromatic hydrocarbyl group having 1 to 24 carbon atoms; and X₁to X₄ independently denote an oxygen atom or a sulfur atom. The fourhydrocarbyl groups, R_(1 to R) ₄, may be identical or different from oneanother.

[0066] Another group of organo-molybdenum compounds useful in thelubricating compositions of this invention are trinuclear (or trimeric)molybdenum compounds, especially those of the formula Mo₃S_(k)L_(n)Q_(z)and mixtures thereof wherein the L are independently selected ligandshaving organo groups with a sufficient number of carbon atoms to renderthe compound soluble in the oil, n is from 1 to 4, k varies from 4 to 7,Q is selected from the group of neutral electron donating compounds suchas water, amines, alcohols, phosphines, and ethers, and z ranges from 0to 5 and includes non-stoichiometric values. At least 21 total carbonatoms should be present among all the ligands' organo groups, such as atleast 25, at least 30, or at least 35 carbon atoms.

[0067] The ligands may be selected from the group consisting of

[0068] and mixtures thereof, wherein X, X₁, X₂, and Y are selected fromthe group consisting of oxygen and sulfur, and wherein R₁, R₂, and R areselected from hydrogen and organo groups that may be the same ordifferent. Preferably, the organo groups are hydrocarbyl groups such asalkyl (e.g. in which the carbon atom attached to the remainder of theligand is primary or secondary), aryl, substituted aryl and ethergroups. More preferably, each ligand has the same hydrocarbyl group.

[0069] The term “hydrocarbyl” as used herein denotes a substituenthaving carbon atoms directly attached to the remainder of the ligand andis predominantly hydrocarbyl in character. Such substituents include thefollowing:

[0070] 1. Hydrocarbon substituents, that is, aliphatic (for examplealkyl or alkenyl), alicyclic (for example cycloalkyl or cycloalkenyl)substituents, aromatic-, aliphatic- and alicyclic-substituted aromaticnuclei, as well as cyclic substituents wherein the ring is completedthrough another portion of the ligand (that is, any two indicatedsubstituents may together form an alicyclic group).

[0071] 2. Substituted hydrocarbon substituents, that is, thosecontaining non-hydrocarbon groups which do not alter the predominantlyhydrocarbyl character of the substituent. Those skilled in the art willbe aware of suitable groups (e.g., halo, especially chloro and fluoro,amino, alkoxyl, mercapto, alkylmercapto, nitro, nitroso, sulfoxy, etc.).

[0072] Importantly, the organo groups of the ligands have a sufficientnumber of carbon atoms to render the compound soluble in the oil. Forexample, the number of carbon atoms in each group will generally rangebetween 1 to 100, preferably from 1 to 30, and more preferably between 4to 20. Preferred ligands include dialkyldithiophosphate, alkylxanthate,carboxylates, dialkyldithiocarbamate (“dtc”), and mixtures thereof. Mostpreferred are the dialkyldithiocarbamates. Those skilled in the art willrealize that formation of the compounds of the present inventionrequires selection of ligands having the appropriate charge to balancethe core's charge (as discussed below).

[0073] Compounds having the formula Mo₃S_(k)L_(n)Q_(z) have cationiccores surrounded by anionic ligands, wherein the cationic cores arerepresented by structures such as

[0074] which have net charges of +4. Electrical neutrality to thetrinuclear molybdenum Mo₃S_(k) species, where k is 4 to 7, is conferredby appropriate choice of anionic and cationic compounds. Fourmonoanionic ligands, e.g. dithiocarbamate, are preferred. Withoutwishing to be bound by any theory, it is believed that two or moretrinuclear cores may be bound or interconnected by means of one or moreligands and the ligands may be multidentate, i.e., having multipleconnections to one or more cores. It is believed that oxygen and/orselenium may be substituted for sulfur in the core(s).

[0075] Oil-soluble trinuclear molybdenum compounds can be prepared byreacting in the appropriate liquid(s)/solvent(s) a molybdenum sourcesuch as (NH₄)₂Mo₃S₁₃.n(H₂O), where n varies between 0 and 2 and includesnon-stoichiometric values, with a suitable ligand source such as atetralkylthiuram disulfide. Other oil-soluble trinuclear molybdenumcompounds can be formed during a reaction in the appropriate solvent(s)of a molybdenum source such as (NH₄)₂Mo₃S₁₃.n(H₂O), a ligand source suchas tetralkylthiuram disulfide, dialkyldithiocarbamate, ordialkyldithiophosphate, and a sulfur-abstracting agent such as cyanideions, sulfite ions, or substituted phosphines. Alternatively, atrinuclear molybdenum-sulfur halide salt such as [M′]₂[Mo₃S₇A₆], whereM′ is a counter ion, and A is a halogen such as Cl, Br, or I, may bereacted with a ligand source such as a dialkyldithiocarbamate ordialkyldithiophosphate in the appropriate liquid(s)/solvent(s) to forman oil-soluble trinuclear molybdenum compound. The appropriateliquid/solvent may be, for example, aqueous or organic.

[0076] The ligand chosen must have a sufficient number of carbon atomsto render the compound soluble in the lubricating composition.

[0077] Trinuclear molybdenum compounds for use in the compositions ofthis invention can be those of the formula Mo₃S₇((alkyl)₂dtc)₄ where thealkyl has about 8 to 18 carbon atoms and the alkyl being preferably a“coco” alkyl chain which is a mixture of chains of varying even numbersof carbon atoms from typically a C₈ to C₁₈ alkyl, mainly C₁₀, C₁₂ andC₁₄ alkyls derived from coconut oil.

[0078] Other examples of molybdenum compounds include a sulfurizedmolybdenum containing composition prepared by (i) reacting an acidicmolybdenum compound and a basic nitrogen compound selected from thegroup consisting of succinimide, a carboxylic acid amide, a hydrocarbylmonoamine, a phosphoramide, a thiophosphoramide, a Mannich base, adispersant viscosity index improver, or a mixture thereof, in thepresence of a polar promoter, to form a molybdenum complex, and (ii)reacting the molybdenum complex with a sulfur-containing compound, tothereby form a sulfur- and molybdenum-containing composition.

[0079] In one embodiment of the present invention, the molybdenumcompound is preferably dinuclear or trinuclear, more preferablytrinuclear.

[0080] In another embodiment of the present invention, the molybdenumcompound, irrespective of its nuclearity, is fully sulfurised, i.e. thecore contains only sulfur as the non-metallic element, for exampleMo₂S₄, Mo₃S₄ and Mo₃S₇.

[0081] In another embodiment of the present invention, the molybdenumcompound is preferably a dithiocarbamate compound, such a dinuclear ortrinuclear molybdenum dithiocarbamate; especially effective compoundsare molybdenum dialkyldithiocarbamate compounds represented by theformula Mo₃S₇((alkyl)₂dtc)₄.

[0082] Colloidal friction reducers may also be used in the presentinvention, such as graphite, borate and molybdenum disulfide that arepresent in the oil composition by dispersion.

[0083] The oil composition may contain a mixture of friction reducers,such as polar compounds that are capable of being adsorbed on a metalsurface, whether organic or organo-metallic, and molybdenum compounds.

[0084] In an embodiment, the friction reducer is an organic polarcompound having an oleophilic hydrocarbyl chain, such as glycerolmonoleate.

[0085] In another embodiment, the friction reducer is a molybdenumcompound.

[0086] The friction reducers are present in an amount sufficient toimprove the fuel economy of the engine being lubricated. The amount istypically from 0.01 to 5.0, preferably 0.05 to 1.5, more preferably 0.1or 0.15 to 0.5, mass %, based on the mass of the oil composition.

[0087] In the instance the friction reducer is a molybdenum compound,the lubricating oil composition preferably contains 5 to 5000, morepreferably 10 to 1000, especially 50 to 750, for example, 75 to 500, ppmof molybdenum by mass, based on the mass of the oil composition. Theamount of molybdenum is measured according to ASTM D5185.

[0088] Detergent Composition

[0089] Detergents may also be present in lubricating oil compositions ofthe present invention.

[0090] A detergent is an additive that reduces formation of pistondeposits, for example high-temperature varnish and lacquer deposits, inengines; it has acid-neutralising properties and is capable of keepingfinely divided solids in suspension. It is based on metal “soaps”, thatis metal salts of organic acids, also known as surfactants herein.

[0091] A detergent comprises a polar head, i.e. the metal salt of theorganic acid, with a long hydrophobic tail for oil solubility.Therefore, the organic acids typically have one or more functionalgroups, such as OH or COOH or SO₃H; and a hydrocarbyl substituent.

[0092] Examples of organic acids include sulphonic acids, phenols andsulphurised derivatives thereof, and carboxylic acids.

[0093] Thus, a detergent composition comprising one or more metal saltsof organic acids may be present, for example, a mixture of metalsulfonate and metal phenate.

[0094] It has been found that a detergent composition comprising a metalsalt of an aromatic carboxylic acid provides improved performance.

[0095] A preferred detergent composition comprises more than 50 mole %of a metal salt of an aromatic carboxylic acid, based on the moles ofthe metal salts of organic acids in the detergent composition.Preferably the proportion of the metal salt of an aromatic carboxylicacid is at least 60 or at least 70 mole %; more preferably at least 80or at least 90 mole %, based on the moles of the metal salts of organicacids in the detergent composition.

[0096] In a most preferred embodiment, the detergent compositioncomprises 100 mole % of a metal salt of an aromatic carboxylic acid,based on the moles of the metal salts of organic acids in the detergentcomposition; that is the detergent composition comprises only aromaticcarboxylic acids as the organic acids.

[0097] The aromatic moiety of the aromatic carboxylic acid can containheteroatoms, such as nitrogen and oxygen. Preferably, the moietycontains only carbon atoms; more preferably the moiety contains six ormore carbon atoms; for example benzene is a preferred moiety.

[0098] The aromatic carboxylic acid may contain one or more aromaticmoieties, such as one or more benzene rings, either fused or connectedvia alkylene bridges.

[0099] The carboxylic moiety may be attached directly or indirectly tothe aromatic moiety. Preferably the carboxylic acid group is attacheddirectly to a carbon atom on the aromatic moiety, such as a carbon atomon the benzene ring.

[0100] More preferably, the aromatic moiety also contains a secondfunctional group, such as a hydroxy group or a sulfonate group, whichcan be attached directly or indirectly to a carbon atom on the aromaticmoiety.

[0101] Preferred examples of an aromatic carboxylic acids are salicylicacids and sulphurised derivatives thereof, such as hydrocarbylsubstituted salicylic acid and derivatives thereof.

[0102] Processes for sulfurizing, for example a hydrocarbyl-substitutedsalicylic acid, are similar to those used for phenols, and are wellknown to those skilled in the art.

[0103] Salicylic acids are typically prepared by carboxylation, forexample, by the Kolbe-Schmitt process, of phenoxides, and in that case,will generally be obtained, normally in a diluent, in admixture withuncarboxylated phenol.

[0104] Preferred substituents in oil-soluble salicylic acids are alkylsubstituents. In alkyl-substituted salicylic acids, the alkyl groupsadvantageously contain 5 to 100, preferably 9 to 30, especially 14 to20, carbon atoms. Where there is more than one alkyl group, the averagenumber of carbon atoms in all of the alkyl groups is preferably at least9 to ensure adequate oil-solubility.

[0105] The detergent composition can comprise metal salts of organicacids other than aromatic carboxylic acids, such as sulfonic acids,phenols and sufurised derivatives thereof, and carboxylic acids. Suchorganic acids are described in WO 97/46643, which is incorporated hereinby reference.

[0106] Each or the metal detergent in the detergent composition may beneutral or overbased, such terms are understood by those skilled in theart.

[0107] The detergents of the present invention may be salts of one typeof organic acid or salts of more than one type of organic acids, forexample hybrid complex detergents. Preferably, they are salts of onetype of organic acid.

[0108] A hybrid complex detergent is where the basic material within thedetergent is stabilised by more than one type of organic acid. It willbe appreciated by one skilled in the art that a single type of organicacid may contain a mixture of organic acids of the same type. Forexample, a sulfonic acid may contain a mixture of sulfonic acids ofvarying molecular weights. Such an organic acid composition isconsidered as one type. Thus, complex detergents are distinguished frommixtures of two or more separate overbased detergents, an example ofsuch a mixture being one of an overbased calcium salicylate detergentwith an overbased calcium phenate detergent.

[0109] The art describes examples of overbased complex detergents. Forexample, International Patent Application Publication Nos.97-46643/4/5/6 and 7 describe hybrid complexes made by neutralising amixture of more than one acidic organic compound with a basic metalcompound, and then overbasing the mixture. Individual basic micelles ofthe detergent are thus stabilised by a plurality of organic acid types.Examples of hybrid complex detergents include calciumphenate-salicylate-sulfonate detergent, calcium phenate-sulfonatedetergent and calcium phenate-salicylate detergent.

[0110] EP-A-0 750 659 describes a calcium salicylate phenate complexmade by carboxylating a calcium phenate and then sulfurising andoverbasing the mixture of calcium salicylate and calcium phenate. Suchcomplexes may be referred to as “phenalates”

[0111] Preferred complex detergents are salicylate-based detergents, forexample, a calcium phenate-salicylate-sulfonate detergent and“phenalates”.

[0112] In the instance where more than one type of organic acids ispresent in a single detergent, the proportion of any one type of organicacid to another is not critical, provided the detergent compositioncomprises the defined proportion of the metal salt of an aromaticcarboxylic acid.

[0113] For the avoidance of doubt, the detergent composition may alsocomprise ashless detergents, i.e. non-metal containing detergents.

[0114] Preferably the detergent composition comprises at least oneoverbased metal detergent.

[0115] A preferred overbased metal detergent comprises one or more metalsalts of aromatic carboxylic acids, preferably one or more metal saltsof salicylic acids.

[0116] Group 1 and Group 2 metals are preferred as metals in thedetergents; more preferably calcium and magnesium, especially calcium ispreferred.

[0117] Detergent compositions comprising at least one calciumsalicylate-based detergent, preferably at least one overbased calciumsalicylate-based detergent, have been found to be particularly effectivein the present invention.

[0118] Applicant, therefore, considers that detergent compositionscomprising only calcium salicylate-based detergents, whether neutral oroverbased, would be advantageous.

[0119] Preferably, the detergent composition is present in the oilcomposition in an amount, based on surfactant content, of at least 5,preferably at least 10, such as at least 20 or at least 30, morepreferably at least 50, most especially at most 75, millimoles ofsurfactant per kilogram of the oil composition (mmol/kg). In anembodiment, the amount of detergent composition, based on surfactantcontent, in the oil composition is 10 to 15 mmol/kg.

[0120] Means for determining the amount of surfactant and the amount ofmetal salt of an aromatic carboxylic acid are known to those skilled inthe art. For example, a skilled person can calculate the amounts in thefinal lubricating oil composition from information concerning the amountof raw materials (e.g. organic acids) used to make the detergent(s) andfrom information concerning the amount of detergent(s) used in the finaloil composition. Analytical methods (e.g. potentiometric titration andchromatography) can also be used to determine the amounts of surfactantand metal salt of an aromatic carboxylic acid.

[0121] It will be appreciated by a skilled person in the art that themethods to determine the amount of metal salts of organic acids (alsoknown as surfactants), including the amount of metal salts of aromaticcarboxylic acids, are at best approximations and that differing methodswill not always give exactly the same result; they are, however,sufficiently precise to allow the practice of the present invention.

[0122] Dispersant Additive

[0123] Dispersant additives maintain oil-insoluble substances, resultingfrom oxidation during use, in suspension in the fluid, thus preventingsludge flocculation and precipitation or deposition on metal parts.So-called ashless dispersants are organic materials which formsubstantially no ash on combustion, in contrast to metal-containing (andthus ash-forming) detergents. Borated metal-free dispersants are alsoregarded herein as ashless dispersants. Suitable dispersants include,for example, derivatives of long chain hydrocarbyl-substitutedcarboxylic acids, in which the hydrocarbyl group has a number averagemolecular weight of less than 15,000, such as less than 5000; examplesof such derivatives being derivatives of high molecular weighthydrocarbyl-substituted succinic acid. Such hydrocarbyl-substitutedcarboxylic acids may be reacted with, for example, a nitrogen-containingcompound, advantageously a polyalkylene polyamine, or with an alcohol.Particularly preferred dispersants are the reaction products ofpolyalkylene amines with alkenyl succinic anhydrides. Examples ofspecifications disclosing dispersants of the last-mentioned type areU.S. Pat. Nos. 3,202,678, 3,154,560, 3,172,892, 3,024,195, 3,024,237,3,219,666, 3,216,936 and BE-A-662 875.

[0124] Alternatively or in addition, dispersancy may be provided bypolymeric compounds capable of providing viscosity index improvingproperties and dispersancy, such compounds are known as multifunctionalviscosity index improvers. Such polymers differ from conventionalviscosity index improvers in that they provide performance properties,such as dispersancy and/or antioxidancy, in addition to viscosity indeximprovement.

[0125] Dispersant olefin copolymers and dispersant polymethacrylates areexamples of multifunctional viscosity index improvers. Multifunctionalviscosity index improvers are prepared by chemically attaching variousfunctional moieties, for example amines, alcohols and amides, ontopolymers, which polymers preferably tend to have a number averagemolecular weight of at least 15,000, such in the range from 20,000 to600,000, as determined by gel permeation chromatography or lightscattering methods. The polymers used may be those described above withrespect to viscosity modifiers. Therefore, amine molecules may beincorporated to impart dispersancy and/or antioxidancy characteristics,whereas phenolic molecules may be incorporated to improve antioxidantproperties. A specific example, therefore, is an inter-polymer ofethylene-propylene post grafted with an active monomer such as maleicanhydride and then derivatized with, for example, an alcohol or amine.

[0126] EP-A-24146 and EP-A-0 854 904 describe examples of dispersantsand dispersant viscosity index improvers, which are accordinglyincorporated herein.

[0127] Heavy duty diesel engine lubricating oil compositions tend torequire higher amount of dispersant than for example a passenger carengine oil composition because more oil-insoluble substances, such assoot, are formed in heavy duty diesel engines. Accordingly, the amountof a dispersant additive, whether in the form of a dispersant additiveand/or a multifunctional viscosity index improver additive, in a heavyduty diesel engine lubricating oil composition is, based on nitrogen,preferably at least 0.06, more preferably at least 0.09, especially atleast 0.12, mass %, based on the mass of the oil composition. The amountof nitrogen derived from the dispersant tends not to be more than 0.2mass %.

[0128] In every instance the oil composition has an amount of phosphorusless than 0.09 mass %, based on the mass of the oil composition, and theoil composition does not contain a dispersant viscosity index improveradditive, the amount of nitrogen in the oil composition is preferably atleast 0.045, more preferably 0.5, such at least 0.055, advantageously atleast 0.06, especially at least 0.065, such as at least 0.08, forexample, at least 0.1, mass %, based on the mass of the oil composition.The amount of nitrogen is preferably at most 0.3, such as at most 0.25or at most 0.2, mass %, based on the mass of the oil composition. Theamount of nitrogen is measured according to ASTM D4629. Preferably, theamount of nitrogen is derived from a dispersant additive, such as apolyisobutenyl succinimide. In the event a dispersant viscosity indeximprover additive is present in the lubricating oil composition, thenamount of nitrogen can be lower than 0.045 mass %, for example, from0.001 to 0.04 mass % based on the mass of the oil composition. In apreferred embodiment, the amount of nitrogen, irrespective of whetherthe oil composition contains dispersant viscosity index improveradditive or not, is at least 0.045 mass %. In the instance the oilcomposition contains a dispersant viscosity index improver additive, theamount of the additive is preferably 0.01 to 5, preferably 0.05 to 3,especially 0.1 to 2, mass %, based on the mass of the oil composition.

[0129] Co-Additives

[0130] Other additives may also be present in the oil composition of thepresent invention.

[0131] Co-additives suitable in the present invention include viscosityindex improvers, corrosion inhibitors, other oxidation inhibitors orantioxidants, rust inhibitors or rust prevention agents, anti-wearagents, pour point depressants, demulsifiers, and anti-foaming agents.

[0132] Viscosity index improvers (or viscosity modifiers) impart highand low temperature operability to a lubricating oil and permit it toremain shear stable at elevated temperatures and also exhibit acceptableviscosity or fluidity at low temperatures. Suitable compounds for use asviscosity modifiers are generally high molecular weight hydrocarbonpolymers, including polyesters, such as polymethacrylates;poly(ethylene-co-propylene) polymers and closely related modifications(so called olefin copolymers); hydrogenated poly(styrene-co-butadiene or-isoprene) polymers and modifications; and esterifiedpoly(styrene-co-maleic anhydride) polymers. Oil-soluble viscositymodifying polymers generally have number average molecular weights of atleast 15,000 to 1,000,000, preferably 20,000 to 600,000, as determinedby gel permeation chromatography or light scattering methods. Thedisclosure in Chapter 5 of “Chemistry & Technology of Lubricants”,edited by R. M. Mortier and S. T. Orzulik, First edition, 1992, BlackieAcademic & Professional, is incorporated herein.

[0133] Corrosion inhibitors reduce the degradation of metallic partscontacted by the lubricating oil composition. Thiadiazoles, for examplethose disclosed in U.S. Pat. Nos. 2,719,125, 2,719,126 and 3,087,932 areexamples of corrosion inhibitors for lubricating oils.

[0134] Oxidation inhibitors, or antioxidants, reduce the tendency ofmineral oils to deteriorate in service, evidence of such deteriorationbeing, for example, the production of varnish-like deposits on metalsurfaces and of sludge, and viscosity increase. Suitable oxidationinhibitors include sulfurized alkyl phenols and alkali or alkaline earthmetal salts thereof; hindered phenols; diphenylamines;phenyl-naphthylamines; and phosphosulfurized or sulfurized hydrocarbons.

[0135] Other oxidation inhibitors or antioxidants which may be used inlubricating oil compositions include oil-soluble copper compounds. Thecopper may be blended into the oil as any suitable oil-soluble coppercompound. By oil-soluble it is meant that the compound is oil-solubleunder normal blending conditions in the oil or additive package. Thecopper may, for example, be in the form of a copper dihydrocarbyl thio-or dithio-phosphate. Alternatively, the copper may be added as thecopper salt of a synthetic or natural carboxylic acid, for example, a C₈to C₁₈ fatty acid, an unsaturated acid, or a branched carboxylic acid.Also useful are oil-soluble copper dithiocarbamates, sulfonates,phenates, and acetylacetonates. Examples of particularly useful coppercompounds are basic, neutral or acidic copper Cu^(I) and/or Cu^(II)salts derived from alkenyl succinic acids or anhydrides.

[0136] Copper antioxidants will generally be employed in an amount offrom about 5 to 500 ppm by weight of the copper, in the finallubricating composition.

[0137] Rust inhibitors selected from the group consisting of nonionicpolyoxyalkylene polyols and esters thereof, polyoxyalkylene phenols, andanionic alkyl sulfonic acids may be used.

[0138] Antiwear agents, as their name implies, reduce wear of metalparts. Zinc dihydrocarbyl dithiophosphates (ZDDPs) are very widely usedas antiwear agents. Examples of ZDDPs for use in oil-based compositionsare those of the formula Zn[SP(S)(OR¹)(OR²)]₂ wherein R¹ and R² containfrom 1 to 18, and preferably 2 to 12, carbon atoms.

[0139] Sulfur- and molybdenum-containing compounds are also examples ofanti-wear additives. Also suitable are ashless phosphorus- andsulfur-containing compounds.

[0140] Pour point depressants, otherwise known as lube oil flowimprovers, lower the minimum temperature at which the fluid will flow orcan be poured. Such additives are well known. Foam control may beprovided by an antifoamant of the polysiloxane type, for example,silicone oil or polydimethyl siloxane.

[0141] A small amount of a demulsifying component may be used. Apreferred demulsifying component is described in EP-A-0 330 522. It isobtained by reacting an alkylene oxide with an adduct obtained byreacting a bis-epoxide with polyhydric alcohol.

[0142] Some of the above-mentioned additives may provide a multiplicityof effects; thus for example, a single additive may act as adispersant-oxidation inhibitor. This approach is well known and need notbe further elaborated herein.

[0143] Preferably an anti-wear additive, such a metaldihydrocarbyldithiophosphate, for example, zincdihydrocarbyidithiophosphate, is present in the lubricating oilcompositions of the present invention.

[0144] When lubricating compositions contain one or more of theabove-mentioned additives, including the detergents, each additive istypically blended into the base oil in an amount which enables theadditive to provide its desired function. Representative effectiveamounts of such additives, when used in lubricants, are as follows: Mass% a.i.* Mass % a.i.* Additive (Broad) (Preferred) Viscosity Modifier 0.01-6  0.01-4 Corrosion Inhibitor  0.01-5  0.01-1.5 OxidationInhibitor  0.01-5  0.01-1.5 Friction Reducer  0.01-5  0.01-1.5Dispersant  0.1-20  0.1-8 Dispersant Viscosity Modifier  0.01-5  0.05-5Detergent  0.01-6  0.01-3 Anti-wear Agent  0.01-6  0.01-4 Pour PointDepressant  0.01-5  0.01-1.5 Rust Inhibitor 0.001-0.5  0.01-0.2Anti-Foaming Agent 0.001-0.3 0.001-0.15 Demulsifier 0.001-0.5  0.01-0.2

[0145] The additives may be incorporated into a base oil in anyconvenient way. Thus, each of the additive can be added directly to theoil by dispersing or dissolving it in the oil at the desired level ofconcentration. Such blending may occur at ambient temperature or at anelevated temperature.

[0146] When a plurality of additives are employed it may be desirable,although not essential, to prepare one or more additive packages (alsoknown as additive compositions or concentrates) comprising theadditives, whereby several additives, with the exception of viscositymodifiers, multifuntional viscosity modifiers and pour pointdepressants, can be added simultaneously to the base oil to form thelubricating oil composition. Dissolution of the additive package(s) intothe lubricating oil may be facilitated by diluent or solvents and bymixing accompanied with mild heating, but this is not essential. Theadditive package(s) will typically be formulated to contain theadditive(s) in proper amounts to provide the desired concentration inthe final formulation when the additive package(s) is/are combined witha predetermined amount of basestock. The nitrogen content of such anadditive concentrate is generally in the range of 0.5 to 1.5, preferablyin the range of 0.7 to 1.0, mass %, based on the mass of the additiveconcentrate. Thus, one or more detergents may be added to small amountsof base oil or other compatible solvents (such as a carrier oil ordiluent oil) together with other desirable additives to form additivepackages containing active ingredients in an amount, based on theadditive package, of, for example, from 2.5 to 90 mass %, and preferablyfrom 5 to 75 mass %, and most preferably from 8 to 60 mass %, ofadditives in the appropriate proportions with the remainder beingdiluent. The final formulations may typically contain 5 to 40 mass % ofthe additive package(s), the remainder being diluent.

[0147] The amount of additives in the final lubricating oil compositionis generally dependent on the type of the oil composition, for example,a heavy duty diesel engine lubricating oil composition has 2 to 20,preferably 5 to 18, more preferably 7 to 16, such as 8 to 14, mass % ofadditives based on the mass of the oil composition.

[0148] Thus, a method of preparing the oil composition according to thepresent invention can involve admixing an oil of lubricating viscosityand one or more of the defined compounds or an additive package thatcomprises one or more of the defined compounds.

[0149] It should be appreciated that interaction may take place betweenany two or more of the additives, including any two or more detergents,after they have been incorporated into the oil composition. Theinteraction may take place in either the process of mixing or anysubsequent condition to which the composition is exposed, including theuse of the composition in its working environment. Interactions may alsotake place when further auxiliary additives are added to thecompositions of the invention or with components of oil. Suchinteraction may include interaction which alters the chemicalconstitution of the additives. Thus, the compositions of the inventioninclude compositions in which interaction, for example, between any ofthe additives, has occurred, as well as compositions in which nointeraction has occurred, for example, between the components mixed inthe oil.

[0150] In this specification:

[0151] The term “comprising” or “comprises” when used herein is taken tospecify the presence of stated features, integers, steps or components,but does not preclude the presence or addition of one or more otherfeatures, integers, steps, components or groups thereof.

[0152] The term “oil-soluble” or “oil-dispersible”, as used herein, doesnot mean that the additives are soluble, dissolvable, miscible orcapable of being suspended in the oil in all proportions. They do mean,however, that the additives are, for instance, soluble or stabledispersible in the oil to an extent sufficient to exert their intendedeffect in the environment in which the oil composition is employed.Moreover, the additional incorporation of other additives such as thosedescribed above may affect the solubility or dispersibility of theadditives.

[0153] “Major amount” means in excess of 50 mass % of the composition.

[0154] “Minor amount” means less than 50 mass % of the composition, bothin respect of the stated additive and in respect of the total mass % ofall of the additives present in the composition, reckoned as activeingredient of the additive or additives.

[0155] “TBN” is Total Base Number as measured by ASTM D2896.

[0156] All percentages reported are mass % on an active ingredientbasis, i.e., without regard to carrier or diluent oil, unless otherwisestated.

[0157] The abbreviation SAE stands for Society of Automotive Engineers,who classify lubricants by viscosity grades.

[0158] The invention is illustrated by, but in no way limited to, thefollowing examples.

EXAMPLES

[0159] Lubricating oil compositions were blended by known methods sothat each composition was an SAE 5W30 lubricating oil composition. Eachoil composition comprised a detergent composition containing salicylatedetergents; a zinc dihydrocarbyl dithiophosphate; and a borateddispersant. Thus, each oil composition was comparable to one anotherbecause they contained identical additives with the exception of Example1 and Example 2, which also contained a friction reducer: Example 1contained as a friction reducer a glycerol monoleate in an amount of 0.3mass %, while Example 2 contained as a friction reducer a trinuclearmolybdenum dithiocarbamate in an amount of 450 ppm of molybdenum.

[0160] The lubricating oil compositions (Comparative Example A, Example1 and Example 2) were tested for fuel economy in a total driveline rigwhich comprised a Volvo FH-12 litre heavy duty diesel engine, togetherwith a transmission including a gearbox and an axle.

[0161] The rig is based upon extensive use of electronic enginemanagement systems, which allows the connection of transmission and to acertain degree transaxles via CAN (Controlled Area Network) as a totaldriveline rig. This rig is described in “Neues F&E-Zentrum fürAntriebsstrang-Schmierung” by Peter Ahrweiler and Gerd Rentel, ATZAutomobiletechnische Zeitschrift, 100 (1998), 3, pages 202-209. One ofthe major benefits of the total driveline rig is in the form of reducederror of measurement of heavy duty diesel fuel economy. Removal of errorsources associated with fleet trials such as driver variation, tyrepressure variation, drive cycle variation and aerodynamic variation isessential if accurate fuel economy measurements are to be made. This isnow possible using the total driveline rig. Historical data has shownthat fuel economy measurements of greater than 0.29% are real at the 95%confidence interval.

[0162] The fuel economy measurements are quoted as an improvement, inpercentage, compared to a lubricating oil composition having the sameadditive components as Comparative Example A, but blended to an SAE15W40 grade.

[0163] Table 1 summarises the results obtained and shows that the use offriction reducers in heavy duty diesel engine lubricating oilcompositions provides an improvement in the fuel economy of the engine:the improvement is about double that achieved by the oil composition notcontaining a friction reducer (compare Comparative Example A withExample 1 or Example 2). Table 1 also provides certain properties of theoil compositions. TABLE 1 Comparative Example A Example 1 Example 2 SAEJ300 classification 5W30 5W30 5W30 Phosphorus, % mass 0.12 0.13 0.12(ASTM D5185) Sulfur, % mass (ASTM D5185) 0.33 0.34 0.41 Nitrogen, mass %0.10 0.10 0.11 Base blend 8.83 8.80 8.89 viscosity @100° C., mm²s⁻¹Improvement in Fuel Economy  0.69² 1.50 1.35

What is claimed is:
 1. A method composition for improving the fueleconomy of a heavy duty diesel engine, which method compriseslubricating said engine with a lubricating oil composition comprising aneffective amount of one or more compounds capable of reducing frictioncoefficients under mixed lubrication or boundary lubrication conditionsin a heavy duty diesel engine lubricating oil composition.
 2. The methodof claim 1 wherein the heavy duty diesel engine is the engine of aland-based vehicle, has a total displacement of at least 6.5 litres anda displacement per cylinder of at least 1.0 litre per cylinder.
 3. Aheavy duty diesel engine lubricating oil composition comprising an oilof lubricating viscosity, in a major amount, and added thereto: (A) aneffective amount of one or more compounds capable of reducing frictioncoefficients under mixed lubrication or boundary lubrication conditions;(B) a minor amount of a detergent composition comprising a metal salt ofan aromatic carboxylic acid; and (C) a minor amount of a dispersantadditive; provided that the lubricating oil composition has a nitrogencontent of at least 0.06 mass %, based on the mass of the composition.4. The oil composition of claim 3, wherein the oil composition satisfiesat least the API CG-4 performance specification and/or the ACEA E2-96performance specification.
 5. The oil composition of claim 3 in the formof an SAE 5W-X or SAE 0W-X lubricating oil composition, where X is anyone of 20, 30, 40 and
 50. 6. The oil composition of claim 4 in the formof an SAE 5W-X or SAE 0W-X lubricating oil composition, where X is anyone of 20, 30, 40 and
 50. 7. The oil composition of claim 3 wherein thebase blend viscosity of the composition is at least 8.2 mm²s⁻¹ at 100°C.
 8. The oil composition of claim 4 wherein the base blend viscosity ofthe composition is at least 8.2 mm²s⁻¹ at 100° C.
 9. The oil compositionof claim 5 wherein the base blend viscosity of the composition is atleast 8.2 mm²s⁻¹ at 100° C.
 10. The oil composition of claim 3 whereinthe or at least one of the compounds has a polar head-group and anoleophilic hydrocarbyl chain.
 11. The oil composition of claim 4 whereinthe or at least one of the compounds has a polar head-group and anoleophilic hydrocarbyl chain.
 12. The oil composition of claim 5 whereinthe or at least one of the compounds has a polar head-group and anoleophilic hydrocarbyl chain.
 13. The oil composition of claim 3 whereinthe or at least one of the compounds is a molybdenum compound.
 14. Theoil composition of claim 4 wherein the or at least one of the compoundsis a molybdenum compound.
 15. The oil composition of claim 5 wherein theor at least one of the compounds is a molybdenum compound.
 16. A heavyduty diesel engine additive concentrate composition comprising a diluentand one or more additives comprising: (A) one or more compounds capableof reducing friction coefficients under mixed lubrication or boundarylubrication conditions; (B) a detergent composition comprising a metalsalt of an aromatic carboxylic acid; and (C) a dispersant additive; eachin such a proportion as to provide a heavy duty diesel enginelubricating oil composition as defined in claim 3 when the oilcomposition contains 2 to 20 mass % of the additives.
 17. A combinationof a heavy duty diesel engine in a land-based vehicle, which engine hasa total displacement of at least 6.5 litres and a displacement percylinder of at least 1.0 litre per cylinder and a lubricating oilcomposition as defined in claim 3.